Electric axial flux machine and drive train for a hybrid-electric or fully-electric motor vehicle

Abstract

The invention relates to an electric axial flux machine (1), in particular for use within a drive train (20) of a hybrid-electric or fully-electric motor vehicle (21), the electric axial flux machine comprising an annular disk-like stator (2) and comprising at least one rotor (4) which is separated from the stator (2) by an air gap (3) and has at least one annular disk-like rotor body (5) which is torque-transmittingly connected to an electrically conductive rotor shaft (6), wherein: on the rotor shaft (6), there is arranged at least one electrically conductive rotor bearing (7) which is designed as a rolling bearing and by means of which the rotor shaft (6) is supported rotatably relative to the stator (2); at least one outer ring (22) of the rotor bearing (7) is connected to the rotor shaft (6), at least one inner ring (23) of the rotor bearing (7) is connected to an electrically conductive end shield (19), the end shield (19) is fixed, by means of at least one axially extending, electrically conductive screw connection (24), to an electrically conductive motor housing (8) in which the stator (2) and the rotor (4) are at least partially received, the stator (2) is electrically insulated with respect to the end shield (19), and the screw connection (24) extends axially through the stator (2); and at least one first electrical insulation element (13) is arranged between the end shield (19) and the screw connection (24), such that the end shield (19) is electrically insulated with respect to the motor housing (8).

Description

[0001] Electric axial flux machine and drive train of a hybrid or fully electric powered motor vehicle

[0002] The present invention relates to an electric axial flux machine, in particular for use within a drive train of a hybrid or fully electric motor vehicle, comprising an annular disk-shaped stator and a rotor separated from the stator by an air gap, with at least one annular disk-shaped rotor body which is coupled to a rotor shaft in a torque-transmitting manner, wherein at least one rotor bearing is arranged on the rotor shaft, by means of which the rotor shaft can be rotatably mounted relative to the stator, wherein the stator and the rotor are received at least partially in a motor housing and the stator is connected to the motor housing via a stator mount.

[0003] Electric motors are increasingly being used for propulsion in motor vehicles to create alternatives to combustion engines that require fossil fuels. Considerable efforts have already been made to improve the everyday usability of electric drives and to offer users the familiar driving comfort.

[0004] A detailed description of an electric drive system can be found in an article in the journal ATZ, Volume 113, 05 / 2011, pages 360-365, by Erik Schneider, Frank Fickl, Bernd Cebulski, and Jens Liebold, entitled: "Highly Integrated and Flexible Electric Drive Unit for E-Vehicles." This article describes a drive unit for one axle of a vehicle, comprising an electric motor arranged concentrically and coaxially to a bevel gear differential. A switchable two-speed planetary gear set is located in the power train between the electric motor and the bevel gear differential, also positioned coaxially to the electric motor and the bevel or spur gear differential. The drive unit has a very compact design and, thanks to the switchable two-speed planetary gear set, allows for a good compromise between climbing ability, acceleration, and energy consumption. Such drive units are also referred to as e-axles.From DE 10 2010 048 837 A1, such a drive device is known, comprising at least one electric motor and at least one planetary differential driven by a rotor of the electric motor. The planetary differential has at least one planet carrier operatively connected to a rotor of the electric motor, first planet gears and second planet gears rotatably mounted on the planet carrier, and a first sun gear and a second sun gear, each of which is operatively connected to an output shaft of the planetary differential. The first planet gears mesh with the first sun gear, and each of the second planet gears meshes with the second sun gear and with one of the first planet gears. Furthermore, the sun gears are arranged coaxially with a rotational axis of the rotor.

[0005] Very strong voltage fluctuations in the power supply of the electric drive generate unwanted electrical currents within the drive. These currents flow through the housing, the shaft, and the rotor bearings, which are damaged by mechanical wear and the current flow itself.

[0006] To prevent this, it is necessary to dissipate this electrical energy. The dissipation of electrical currents via the shaft into the housing is already known in the art. For this purpose, grounding brushes or radially acting grinding elements (carbon brushes) are known, which serve to ground the rotor shaft. Furthermore, axially acting shaft grounding systems are known. These grounding and / or insulating elements prevent the electrical voltage induced in the mechanical structural elements of the electric motor from discharging through the bearings or being transferred to adjacent components of the electric motor.

[0007] For example, publication CN 104 037 985 describes an antistatic discharge device for the rotor of an electric motor. The antistatic discharge device comprises a grounding pin located in a bore at the rear end of the motor's rotor spindle. For grounding and electrical discharge of the rotor spindle, the grounding pin is screwed to the electric motor housing. Axial flux machines are also increasingly used in the aforementioned e-axles. An axial flux machine is a dynamoelectric machine in which the magnetic flux between the rotor and stator runs parallel to the rotor's axis of rotation. Often, both the stator and rotor are largely disk-shaped. Axial flux machines are particularly advantageous when the available axial installation space is limited in a given application.This is often the case, for example, with both of the electric drive systems for electric vehicles described at the beginning. Besides the shorter axial length, another advantage of the axial flux machine lies in its comparatively high torque density. This is due to the larger air gap area available within a given installation space compared to radial flux machines. Furthermore, a smaller iron volume is required compared to conventional machines, which has a positive effect on the machine's efficiency.

[0008] For the bearings of such an axial flux machine, in addition to mechanical wear from shaft rotation, electrical currents flowing from the rotor shaft to ground via the bearings, as already explained, are another cause of wear. Stresses of a certain magnitude can then overcome the insulating properties of the bearing lubrication, generating sparks that can lead to pitting, surface striations, fusion craters, and ultimately to premature failure of the bearings and the motor. A bearing stress, i.e., the stress between the two bearing shells, is usually correlated with a shaft stress, i.e., the stress between the shaft and ground.

[0009] Due to capacitive coupling between the stator winding and the rotor, and the high-frequency control of the stator phases, a voltage potential develops at the rotor bearings. This potential can damage the bearings via so-called discharge currents. As countermeasures, as already explained above, the bearings are insulated (e.g., using ceramic rolling elements) and / or the shaft is grounded by means of a sliding grounding contact (electrically parallel to the bearings). The object of the invention is to provide a rotor for an axial flux machine in which the shaft voltage and the resulting bearing currents are reduced. Furthermore, the invention aims to realize an optimized axial flux machine and an optimized drive train for a motor vehicle.

[0010] This problem is solved by an electric axial flux machine, particularly for use within a powertrain of a hybrid or fully electric motor vehicle, comprising an annular disk-shaped stator and at least one rotor separated from the stator by an air gap, with at least one annular disk-shaped rotor body which is connected to an electrically conductive rotor shaft in a torque-transmitting manner, wherein at least one electrically conductive rotor bearing designed as a rolling bearing is arranged on the rotor shaft, by means of which the rotor shaft is rotatably mounted relative to the stator, wherein at least one outer ring of the rotor bearing is connected to the rotor shaft and at least one inner ring of the rotor bearing is connected to an electrically conductive bearing shield, and the bearing shield is fixed to an electrically conductive motor housing by means of at least one axially extending, electrically conductive screw connection.in which the stator and the rotor are at least partially received, and the stator is electrically insulated from the bearing shield, and the stator is axially penetrated by the screw connection, wherein at least a first electrical insulating element is arranged between the bearing shield and the screw connection, so that the bearing shield is electrically insulated from the motor housing.

[0011] This combination of features offers the advantage of achieving complete isolation of the rotor from the rest of the system. This is particularly important because, by design, electric motors, especially those used within the powertrain of hybrid or fully electric vehicles, can transmit very high voltages to the rotor shaft. The use of an insulating element between the bearing shield and the motor housing ensures reliable electrical isolation without the need for expensive ceramic ball bearings. This prevents the dissipation of high currents via the rotor shaft ground, thus increasing the efficiency and operational reliability of the axial flux machine. Furthermore, this electrical isolation of the rotor from the motor housing effectively prevents parasitic currents from flowing through critical components of the axial flux machine, particularly the rotor bearing.This reduces the load on unwanted return current paths, which increases the service life of the rotor and gearbox bearings and reduces the risk of exceeding EMC limits.

[0012] First, the individual elements of the claimed invention are explained in the order in which they are mentioned in the claim set, and subsequently, particularly preferred embodiments of the invention are described.

[0013] Axial flux machine

[0014] For the purposes of this patent application, an axial flux machine is an electrical machine in which the magnetic flux is axial, i.e., parallel to the axis of rotation. The function of the axial flux machine is based on the interaction between the magnetic field of the stator and the rotor, which is rotated through the air gap. This interaction converts electrical current into mechanical rotational motion, which can be transmitted via the rotor shaft, for example, to a gearbox. This design enables a compact and efficient conversion of electrical energy into mechanical power, which is particularly advantageous for use in vehicle propulsion systems.

[0015] An axial flux machine comprises an annular stator and a rotor separated by an air gap. The stator is preferably mounted in a motor housing and electrically insulated to minimize parasitic currents. The rotor, also annular, is torque-transmitting and coupled to a rotor shaft. This rotor shaft is rotatably mounted via rotor bearings, preferably within the motor housing. The stator is further preferably fixed in the motor housing by means of a special receptacle, with electrical insulation elements ensuring that both the stator and the rotor remain electrically insulated from the housing.

[0016] Depending on the application, it can be advantageous to design an axial flux machine in an I-arrangement or an H-arrangement. In an I-arrangement, the rotor is arranged axially next to a stator or between two stators. In an H-arrangement, two rotors are arranged on opposite axial sides of a stator. The axial flux machine according to the invention is preferably configured in an H-arrangement. In principle, it is also conceivable that the axial flux machine consists of exactly one stator and exactly one rotor.

[0017] In principle, it is also possible for multiple rotor-stator configurations of I-type and / or H-type to be arranged axially side by side. It would also be possible in this context to arrange several I-type rotor-stator configurations side by side in the axial direction. In particular, it is also preferred that the H-type and / or I-type rotor-stator configurations are essentially identical, so that they can be assembled modularly into a complete configuration. Such rotor-stator configurations can, in particular, be arranged coaxially to one another and be connected by a common rotor shaft or by several rotor shafts.

[0018] In particular, the electric machine is dimensioned such that vehicle speeds greater than 50 km / h, preferably greater than 80 km / h, and especially greater than 100 km / h, can be achieved. The electric motor is particularly preferably configured to have a power output greater than 30 kW, preferably greater than 50 kW, and especially greater than 70 kW. It is further preferred that the electric machine provides rotational speeds greater than 5,000 rpm, particularly preferably greater than 10,000 rpm, and most preferably greater than 12,500 rpm.

[0019] The axial flux machine preferably also includes a control unit. The control unit can particularly preferably comprise power electronics for supplying current to the stator or rotor. Power electronics are preferably a combination of various components that control or regulate a current to the electric machine, preferably including the necessary peripheral components such as cooling elements or power supplies. In particular, the power electronics contain one or more power electronic components configured for controlling or regulating a current. These are particularly preferably one or more power switches, e.g., power transistors. The power electronics particularly preferably have more than two, and particularly preferably three, separate phases or current paths, each with at least one dedicated power electronic component.The power electronics are preferably designed to control or regulate a power output per phase with a peak power, preferably continuous power, of at least 1,000 W, preferably at least 10,000 W, and particularly preferably at least 100,000 W.

[0020] For the purposes of this application, motor vehicles are defined as land vehicles that are moved by mechanical power and are not bound to railway tracks. A motor vehicle may be selected, for example, from the groups of passenger cars, trucks, mopeds, light vehicles, motorcycles, buses, or tractors.

[0021] stator

[0022] For the purposes of this patent application, a stator is the stationary part of an electric axial flux machine that generates or conducts a magnetic field to enable the rotating motion of the rotor. The function of the stator thus includes, among other things, generating a stable and strong magnetic field that sets the rotor in motion.

[0023] The stator consists of a ring-shaped body mounted in a motor housing. To minimize parasitic currents and maximize machine efficiency, the stator is advantageously electrically insulated. This can be achieved, for example, by using special insulating elements that separate the stator from the housing and other electrical components.

[0024] The stator of the electric axial flux machine according to the invention preferably comprises a stator body with several circumferentially arranged stator windings. The stator body can be formed as a single piece or segmented in the circumferential direction. The stator body can be formed from a stator lamination stack with several laminated layers of electrical steel. Alternatively, the stator body can also be formed from a pressed soft magnetic material, such as the so-called SMC material (Soft Magnetic Compound).

[0025] For the purposes of this patent application, a rotor is the moving part of an electric axial flux machine that interacts with the stator and delivers mechanical energy by generating torque. The rotor's function is to generate rotary motion through interaction with the stator's magnetic field. This rotary motion is transmitted via the rotor shaft to a gear assembly or directly to the output shaft. The rotor thus contributes significantly to the performance and efficiency of the axial flux machine.

[0026] The rotor comprises an annular rotor body separated from the stator by an air gap. This rotor body is coupled to a rotor shaft for torque transmission. The rotor shaft is rotatable via rotor bearings, preferably mounted within the motor housing, thus ensuring low-friction rotation.

[0027] Rotor shaft

[0028] For the purposes of this patent application, a rotor shaft is a mechanical component of an axial flux machine that connects the rotor body to other drive components and transmits the generated torque. The function of the rotor shaft thus includes, among other things, transmitting the torque generated by the rotor to other mechanical components, such as a gear assembly or directly to an output shaft.

[0029] The rotor shaft consists of a preferably cylindrical shaft that is rigidly connected to the rotor body. It transmits torque and enables the rotor to rotate within the motor housing. The rotor shaft is advantageously supported in rotor bearings, which allow for low-friction and precise rotation. These bearings can be integrated into the motor housing, for example, by means of a bearing shield.

[0030] There are various conceivable designs for the rotor shaft, which can vary depending on the specific requirements of the application. Regarding the choice of material, the rotor shaft can be manufactured from different metals, with high-strength steels or light metal alloys being advantageously used to achieve an optimal strength-to-weight ratio. A preferred embodiment could also include the use of composite materials, which offer high strength at low weight while simultaneously improving vibration damping.

[0031] In terms of design, the rotor shaft can be hollow or solid. A hollow rotor shaft offers the advantage of reduced weight and can accommodate additional features such as cable routing or coolant passages. A solid rotor shaft, on the other hand, offers maximum strength and rigidity, which is particularly advantageous in high-performance applications. Furthermore, the rotor shaft can be treated with special coatings or surface finishes to enhance wear and corrosion resistance.

[0032] Rotor bearings

[0033] For the purposes of this patent application, a rotor bearing is a mechanical component that rotatably supports the rotor shaft of an axial flux machine, particularly within the motor housing, and enables low-friction rotation. The rotor bearing can also help to reduce vibrations and mechanical stresses caused by the rotation of the rotor.

[0034] The rotor bearing preferably consists of an inner and an outer ring, between which rolling elements are located that absorb the loads and enable low-friction rotation. These rolling elements can be made of various materials, with electrically conductive materials such as steel being advantageously used. Particularly preferably, the rolling elements are not made of ceramic, which reduces the cost of the rotor bearing.

[0035] There are various conceivable designs for rotor bearings, which can vary depending on the specific requirements of the application. A preferred design is the double-row rolling bearing, which, due to its construction, offers higher load-carrying capacity and stability. Double-row rolling bearings can be designed as ball bearings or roller bearings, with each variant offering specific advantages. Ball bearings offer high speed capability and good radial and axial load-carrying capacity, while roller bearings offer higher load-carrying capacity and stiffness.

[0036] Motor Housing: For the purposes of this patent application, a motor housing is the outer structure of an electric machine that encloses and protects the internal components, such as the stator and rotor, at least partially. A key function of the motor housing is to protect the internal components from external influences such as dust, moisture, and mechanical damage. Furthermore, the housing serves as a mounting point for the stator and rotor bearings, ensuring the correct alignment and stability of these components. The motor housing can also help dissipate the heat generated during machine operation, thereby improving thermal efficiency.

[0037] The motor housing preferably comprises a housing base and can advantageously be made of a metallic material. It is preferably formed from a metallic casting material such as gray cast iron or cast steel, as these materials offer high strength and durability. It is also possible to manufacture the housing entirely or partially from plastic to save weight and to meet specific application requirements. The housing can be of a single piece or in multiple parts, with a multi-part design facilitating easier assembly and maintenance of the internal components.

[0038] A preferred embodiment of the housing could comprise a pot-shaped housing body that can be closed with a housing lid. This design provides robust and tight shielding of the internal components while also facilitating assembly and disassembly. Another advantageous variant could include the integration of cooling fins or a cooling system to improve heat dissipation and reduce the operating temperature of the machine.

[0039] The housing may also include special seals or gaskets to prevent the ingress of dirt and moisture, thus extending the machine's service life. Other possible designs could include the use of sound-absorbing materials or structures to reduce noise emissions during operation.

[0040] Coupling section For the purposes of this patent application, a coupling section is a specific area of ​​the rotor shaft that serves to transmit the torque to another mechanical component, such as a connecting element or a gear arrangement.

[0041] The coupling section is designed to ensure a torque-transmitting and reliable connection between the rotor shaft and the component to be coupled. This can be achieved through various mechanical joining techniques or even a material bond. An advantageous design of the coupling section can be a toothed connection, which enables high torque transmission and precise alignment. In this toothed connection, the teeth of the rotor shaft engage with corresponding teeth of the component to be coupled, resulting in secure and efficient power transmission. The coupling section can be formed integrally with the rotor shaft, particularly monolithically. Alternatively, the coupling section can be designed as a separate component that is torque-transmitting and coupled to the rotor shaft, for example, in the form of a gear.

[0042] There are several conceivable embodiments of the coupling section, which can vary depending on the specific requirements of the application. One preferred embodiment could be a splined connection, in which the rotor shaft is inserted into a corresponding opening in the component to be coupled. This design offers the advantage of easy assembly and disassembly, which simplifies maintenance.

[0043] Another advantageous variant of the coupling section could be designed as an internal gear, where the gear teeth are located inside a bore in the rotor shaft and engage with corresponding external gear teeth on the component to be coupled. This design offers a compact and space-saving solution, which is particularly advantageous in confined installation spaces. Alternatively, the coupling section can also be designed as an external gear, where the gear teeth are located on the outside of the rotor shaft and engage with corresponding internal gear teeth on the component to be coupled. This design enables high torque transmission and provides a robust and durable connection.

[0044] Additionally, embodiments of the coupling section may include special surface treatments or coatings to increase wear resistance and corrosion resistance. These measures contribute to improving the service life and reliability of the connection.

[0045] Connection element

[0046] For the purposes of this patent application, a connecting element is a mechanical component that serves to connect the rotor shaft to another drive component, such as a gearbox assembly.

[0047] The connecting element is designed to ensure a torque-transmitting and reliable connection between the rotor shaft and the component to be coupled. This connection can be achieved through various mechanical joining techniques that guarantee high stability and efficiency. One advantageous design of the connecting element could be a toothed joint, where the teeth of the connecting element engage with corresponding teeth on the rotor shaft or the component to be coupled. This design offers high torque transmission and a precise mechanical connection.

[0048] There are various conceivable designs for the connecting element, which can vary depending on the specific requirements of the application. One preferred design could be a splined connection. In this design, the connecting element is inserted into a corresponding opening in the component to be coupled, with the splines ensuring a secure and simple connection. This design facilitates assembly and disassembly and is particularly easy to maintain.

[0049] Another advantageous variant of the connecting element could be designed as an internal toothing, where the toothing is located inside a bore of the connecting element and engages with corresponding external teeth on the rotor shaft or another component. This design allows for a compact and space-saving solution, which is advantageous in confined installation spaces.

[0050] Alternatively, the connecting element can also be designed as an external toothing, where the teeth are located on the outside of the connecting element and engage with corresponding internal teeth on the rotor shaft or another component. This design offers a robust and durable connection and enables high torque transmission.

[0051] A particularly advantageous embodiment of the connection element is the gearbox input shaft. In this variant, the connection element is directly connected to a gearbox assembly, thereby efficiently transferring the torque generated by the rotor shaft into the gearbox. This design offers direct and efficient power transmission and is particularly suitable for applications with high performance requirements.

[0052] Additionally, embodiments of the connecting element can include special surface treatments or coatings to increase wear resistance and corrosion resistance. These measures contribute to improving the service life and reliability of the connection.

[0053] Stator mount

[0054] For the purposes of this patent application, a stator mount is a mechanical structure in and / or on the motor housing that securely and precisely holds the stator in position. The function of the stator mount is therefore, in particular, to fix the stator in the correct position. The firm anchoring of the stator enables precise and stable alignment of the magnetic field, which increases the efficiency and performance of the axial flux machine.

[0055] The stator mount consists of a holding device that is firmly connected to the motor housing and surrounds, extends through, or supports the stator. Several possible embodiments of the stator mount exist, which can vary depending on the specific requirements of the application. A preferred embodiment could include an axially extending screw connection that allows for secure and adjustable mounting of the stator. This design offers the advantage of simple assembly and adjustment, which facilitates maintenance and replacement of the stator.

[0056] Another advantageous embodiment of the stator mounting could be designed as a flange connection, in which the stator is attached to the motor housing via flanges and bolts. This design offers a robust and durable connection and enables efficient transmission of mechanical forces.

[0057] Furthermore, the stator mount could also include a clampable holding device, in which the stator is held in position by clamping or clamping mechanisms. This variant allows for quick and easy installation and removal of the stator, which is particularly advantageous in applications with frequent maintenance requirements.

[0058] Additionally, stator mounting designs can incorporate special insulating elements to improve the electrical isolation between the stator and the motor housing. These elements can be made of materials such as ceramic or plastic and contribute to increasing the service life and reliability of the axial flux machine.

[0059] Insulation element

[0060] For the purposes of this patent application, an insulating element is a component used to isolate electrical conductors and components from one another in order to prevent electrical short circuits, flashovers, and other unwanted electrical connections. The function of the insulating element is therefore, in particular, to create a reliable electrical barrier that allows current to flow only along designated paths and prevents unwanted electrical currents from flowing through the mechanical connection points. This helps to avoid damage to other machine components and to comply with EMC limits, thus ensuring the operational safety and efficiency of the machine. The design of the insulating element varies depending on the specific application and requirements. In principle, it can be made of various materials that exhibit high electrical insulation capacity and mechanical stability.Materials such as ceramics, plastics or coated metals are preferred.

[0061] For the purposes of this patent application, a bearing shield is an electrically conductive component that serves to support the bearing of the rotor shaft in an electric axial flux machine and to establish a connection between the bearing and the motor housing. The function of the bearing shield is therefore, in particular, to accommodate the rotor bearing and fix it relative to the motor housing. It can also be combined with insulating elements to ensure electrical isolation from the motor housing. This combination enables efficient transmission of mechanical forces and reliable electrical insulation.

[0062] The bearing shield is designed to provide a robust and stable platform for the rotor bearing. Depending on the specific requirements of the machine, the bearing shield can be constructed differently. One possible design is a flat, disc-shaped component with holes or recesses for mounting screw connections and insulating elements. This design allows for easy assembly and disassembly of the bearing shield, as well as precise alignment of the rotor bearing.

[0063] In another embodiment, the bearing shield can be designed as a more complex component with integrated cooling structures or reinforcing ribs to improve heat dissipation and increase mechanical strength. This design is particularly advantageous for applications subject to high thermal and mechanical loads.

[0064] Another conceivable embodiment is the modular bearing shield, in which individual components of the bearing shield can be manufactured and assembled separately. This allows for flexible adaptation to different design requirements and facilitates maintenance and replacement of parts.

[0065] One design of the bearing shield consists of a disc and an attached cylindrical tube, which serves as a flange and on which the bearing seat is located. This tube extends axially from the disc and provides an additional surface for the bearing seat on the cylindrical tube, thus ensuring a precise fit for the rotor bearing. This design of the bearing shield offers several advantages. A significant advantage of this disc / cylinder tube design is that the disc and the cylindrical tube can be manufactured separately. This reduces manufacturing costs, as the individual components can be produced and then assembled independently. Separate manufacturing also allows for better quality control and greater production flexibility, resulting in increased efficiency and cost savings.The bearing seat provided on the cylinder tube also ensures precise and firm support of the rotor, which increases the operational safety and efficiency of the machine.

[0066] Regarding materials, the bearing shield can be made of various metals such as aluminum, steel, or a metal alloy. Aluminum offers the advantage of low weight and good thermal conductivity, while steel ensures high strength and rigidity. Metal alloys can combine specific properties to optimally meet the requirements of the axial flux machine.

[0067] Advantageous embodiments of the invention

[0068] Advantageous embodiments of the invention are specified in the dependent claims. The features listed individually in the dependent claims can be combined in a technologically meaningful manner and can define further embodiments of the invention. Furthermore, the features specified in the claims are specified and explained in more detail in the description, which also presents further preferred embodiments of the invention. Advantageously, the invention can also be further developed such that, in the area where the screw connection passes through the stator, the stator is electrically insulated from the screw connection. This further contributes to the complete isolation of the rotor from the rest of the system and prevents the risk of electrical breakdowns.It is also possible to implement electrical insulation only in the current flow path between the bearing shield and the motor housing, without necessarily requiring electrical insulation of the entire stator. This leads to efficient use of insulation material, as only the areas that are actually required are insulated. This reduces material costs and simplifies the design of the axial flux machine, while simultaneously ensuring complete isolation of the rotor from the rest of the system.

[0069] According to an advantageous embodiment of the invention, the stator can be provided with a BVR value greater than 40%, preferably greater than 50%, and most preferably greater than 60%. This characteristic contributes to the improved thermal and electrical performance of the axial flux machine and reduces the risk of electrical short circuits or damage to components not designed for high currents. The BVR value, also known as the Bearing Voltage Ratio (BVR), describes the percentage of the stator voltage that is transferred to the rotor. This value is a measure of the electrical coupling between the stator and the rotor and indicates how efficiently the voltage transfer between these two components occurs. A higher BVR value means that a larger proportion of the stator voltage is transferred to the rotor, indicating stronger electrical coupling.This is particularly relevant in applications where high parasitic currents can occur, as a higher BVR value indicates that more voltage is being applied to the rotor, which can potentially lead to higher parasitic currents. Careful management of the BVR value is therefore crucial to avoid undesirable effects such as electrical short circuits or component damage.

[0070] It can also be advantageous to design the screw connection with a screw and a screw head, with the first electrical insulation element positioned between the screw head and the bearing shield. This combination of features offers the advantage of reliable electrical insulation due to the positioning of the insulation element between the screw head and the bearing shield. Additionally, this arrangement enables a cost-effective fastening method using standard components, thus avoiding expensive special components. This reduces the overall cost of the axial flux machine and simplifies manufacturing and maintenance. The use of standard components increases component availability and optimizes logistics, further improving the machine's economic efficiency.

[0071] Advantageously, the invention can also be further developed such that the stator has at least one hollow cylindrical and electrically conductive spacer extending axially through the stator, which is axially supported on one side against the housing and / or on the other side axially against the bearing shield, wherein the spacer is penetrated by the screw connection and a second electrical insulating element is arranged between the bearing shield and the spacer, so that the bearing shield is electrically insulated from the spacer. The hollow cylindrical spacer provides a stable mechanical connection and simultaneously ensures effective electrical insulation. This contributes to the complete isolation of the rotor and avoids the need for rotor shaft grounding even when a spacer is used.This measure increases the operational reliability of the axial flux machine and reduces the risk of electrical short circuits.

[0072] According to a further preferred embodiment of the invention, it is also provided that, in a plurality of screw connections, at least one electrical insulating element is arranged between the bearing shield and the respective screw connection, so that the bearing shield is electrically insulated from the motor housing. This combination of features offers the advantage that, when using multiple screw connections with respective insulating elements, uniform electrical insulation is ensured across the entire connection. This increases the reliability of the insulation and minimizes the risk of electrical faults that could arise from individual uninsulated connections. Furthermore, assembly flexibility is increased, since each screw connection can be individually insulated and adapted.It can also be advantageous for a majority of the bolted connections, preferably all of them, to extend through a spacer, which further improves the mechanical stability and electrical insulation of the axial flux machine. The even distribution of mechanical loads and the avoidance of localized stresses extend the machine's service life. Furthermore, the combination of spacers and insulating elements optimizes electrical insulation.

[0073] Furthermore, it is preferred that the first electrical insulating element and / or the second electrical insulating element is each designed as a disc-shaped insulating element, in particular as a ceramic disc, plastic disc, electrically insulating metal disc, or coated plastic disc. These materials offer high electrical insulation values ​​and sufficient resistance to mechanical stresses and temperature fluctuations. This leads to increased reliability and longevity of the axial flux machine, especially under demanding operating conditions. Another advantage is the use of standard components. This enables cost-effective manufacturing and maintenance, as these components are readily available and generally relatively inexpensive.

[0074] According to a further preferred embodiment of the invention, the first electrical insulation element and / or the second electrical insulation element can be designed as a shim disk. Designing an insulation element as a shim disk offers the advantage of enabling axial tolerance compensation. This allows for precise adjustment of the distances between the individual components of the axial flux machine. Furthermore, the use of the shim disk can contribute to the reduction of mechanical stresses and vibrations.

[0075] In a further preferred embodiment of the invention, the first electrical insulation element and / or the second electrical insulation element are designed in a sleeve-like shape, thereby ensuring particularly effective electrical insulation. Sleeve-like insulation elements also offer easy handling and assembly, which simplifies the production processes of the axial flux machine and increases its reliability. Furthermore, the sleeve-like insulation elements contribute to the axial lengthening of creepage distances, which further reduces the risk of electrical flashovers and increases the operational safety of the axial flux machine.

[0076] According to a further particularly preferred embodiment of the invention, the motor housing may comprise a pot-shaped housing base and a housing cover by means of which the housing base can be closed, wherein the stator mount extends at least partially through the housing cover and at least partially through the housing base, and the second electrical insulation element is positioned between the housing cover and the housing base and / or the stator, so that the housing cover is electrically isolated from the housing base. This ensures continuous electrical insulation between the housing cover and the housing base, which increases the efficiency of the insulation and improves protection against electrical short circuits.

[0077] Furthermore, the invention can be further developed such that the rotor bearing is designed as a rolling bearing with electrically conductive rolling elements, particularly made of steel, which offers the advantage of a more cost-effective design since expensive ceramic rolling elements can be dispensed with. This choice of materials enables more economical production and maintenance of the axial flux machine without compromising the mechanical robustness and electrical conductivity of the bearing. This improves the overall economic efficiency of the system while maintaining performance and reliability.

[0078] In a further preferred embodiment of the invention, the rotor bearing can also be electrically connected to the motor housing, in particular to the housing cover and / or the end shield. The electrical conductivity of the rotor bearing and its connection to the motor housing, especially to the housing cover and / or the end shield, offers the advantage that electrically conductive materials can be used along a possible current path from the rotor shaft via the rotor bearing to the motor housing. These materials can generally be provided cost-effectively and do not require additional electrical insulation. This leads to a more economical manufacture of the axial flux machine without compromising the electrical and mechanical integrity of the system.

[0079] It may also be advantageous to further develop the invention in such a way that the connecting element is a gearbox input shaft, via which the rotor shaft can be coupled to a gearbox arrangement.

[0080] Finally, the invention can also advantageously be implemented such that the powertrain of a hybrid or fully electric motor vehicle comprises an axial flux machine according to any one of claims 1-9. The powertrain of a hybrid or fully electric motor vehicle comprising the axial flux machine according to the invention benefits from the advantages described above. The improved electrical insulation and the efficient avoidance of parasitic currents contribute to the overall reliability and performance of the powertrain, ultimately leading to a longer service life and higher efficiency of the motor vehicle.

[0081] An electrically operated drive train comprises an electric machine and preferably a gearbox coupled to the electric machine. The gearbox and the electric machine form a single structural unit. This unit can, for example, be formed by a drive train housing in which the gearbox and the electric machine are jointly accommodated.

[0082] The transmission arrangement can be coupled, in particular, to the electric machine, which is designed to generate drive torque for the motor vehicle. The drive torque is preferably a main drive torque, so that the motor vehicle is driven exclusively by the drive torque. The transmission arrangement is preferably designed as a planetary gear set. Most preferably, the planetary gear set is wet-running. The invention will now be explained in more detail with reference to the figures, without limiting the general concept of the invention.

[0083] It shows:

[0084] Figure 1 shows a first embodiment of an axial flux machine in an axial sectional view,

[0085] Figure 2 shows a second embodiment of an axial flux machine in an axial sectional view.

[0086] Figure 3 shows a motor vehicle with an electrically powered drivetrain.

[0087] Figure 1 shows a first embodiment of an electric axial flux machine 1 for use within a powertrain 20 of a hybrid or fully electric motor vehicle 21, as is also shown by way of example in Figure 3.

[0088] The axial flux machine 1 comprises an annular disk-shaped stator 2 and a rotor 4a, 4b separated from the stator 2 by an air gap 3, with at least one annular disk-shaped rotor body 5a, 5b each, which is coupled to an electrically conductive rotor shaft 6 for torque transmission and which rotates about the axis of rotation 18. The axial flux machine 1 shown is therefore configured in an H-configuration.

[0089] An electrically conductive rotor bearing 7 is arranged on the rotor shaft 6, allowing the rotor shaft 6 to be rotatably mounted relative to the stator 2. The rotor bearing 7 is designed as a rolling bearing with electrically conductive rolling elements 16, in particular made of steel.

[0090] The outer rings 22 of the rotor bearing 7 are connected to the rotor shaft 6, while the inner rings 23 of the rotor bearing 7 are connected to an electrically conductive bearing shield 19. An electrical current path can thus be defined via the rolling elements 16 from the rotor shaft 6 through the rotor bearing 7 to the bearing shield 19. In the illustrated embodiment, the bearing shield 19 is designed in two parts: an annular disc-like first part 19a and a hollow cylindrical second part 19b, which provides a bearing seat and supports the inner rings 23.

[0091] The bearing shield 19 is fixed to an electrically conductive motor housing 8 by means of at least one axially extending, electrically conductive screw connection 24. The stator 2 and the rotor 4 are at least partially housed within the motor housing 8. The screw connection 24 axially penetrates the stator 2 to secure the bearing shield 19 to the motor housing 8.

[0092] The stator 2 and the rotor 4 are housed in a motor casing 8, and the stator 2 is connected to the motor casing 8 via a stator mount 12. The stator 2 is electrically insulated from the motor casing 8 and has a BVR value of approximately 65%.

[0093] An electrical insulation element can be arranged between the coupling section 9 of the rotor shaft 6 and a connection element 10 that is connected to the coupling section 9 in a torque-transmitting manner, thus electrically isolating the connection element 10 from the coupling section 9. In the embodiment shown, the connection element 10 is a gearbox input shaft via which the rotor shaft 6 is coupled to a gearbox assembly 17.

[0094] The rotor 4 is also electrically insulated from the motor housing 8. Figure 1 clearly shows that a grounding element, such as a brush element or grounding bearing, connecting the rotor 4 to the mass of the housing 8 has been omitted.

[0095] A first electrical insulating element 13 is arranged between the bearing shield 19 and the screw connection 24, so that the bearing shield 19 is electrically insulated from the motor housing 8. The stator 2 also has at least one hollow cylindrical spacer 28 extending axially through the stator 2, which is supported axially on one side against the housing 8 and on the other side axially against the bearing shield 19, with the screw connection 24 passing through the spacer 28. In the embodiment of Figure 1, the spacer 28 is electrically insulated, i.e., it does not provide a current path between the bearing shield 19 and the motor housing 8.

[0096] The screw connection 24 has a screw 26 with a screw head 27 and the first electrical insulation element 13 is positioned between the screw head 27 and the bearing shield 19, thereby interrupting a possible current path between the screw connection 24 and the bearing shield 19.

[0097] Figure 2 shows another embodiment of the axial flux machine 1 in which the spacer 28 is electrically conductive. To prevent current flow between the bearing shield 19 and the motor housing 8 in this embodiment, a second electrical insulating element 11 is arranged between the bearing shield 19 and the spacer 28, so that the bearing shield 19 is also electrically insulated from the spacer 28. Additionally, in the penetration area 29 of the screw connection 24 through the stator 2, the stator 2 is electrically insulated from the screw connection 24.

[0098] The electrical insulating elements 11, 13 are each designed as a disc-shaped insulating element, for example as a ceramic disc, a plastic disc, an electrically insulating metal disc, or a coated plastic disc. A design as a shim disc is also conceivable.

[0099] In the embodiment shown in Figures 1-2, the motor housing 8 has a pot-shaped housing base and a housing cover (not shown) by means of which the housing base can be closed.

[0100] The depicted design of the axial flux machine 1 effectively and cost-efficiently prevents leakage currents, particularly those flowing through the rotor bearing 7. The necessary insulation elements 11, 13 are inexpensive to manufacture, thus eliminating the need for costly measures such as the use of ceramic rolling elements in the bearings or an earthing bearing. The invention is not limited to the embodiments shown in the figures. The preceding description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features.

[0101] If the patent claims and the preceding description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a hierarchy.

[0102] List of reference signs

[0103] 1 Axial flux machine

[0104] 2 Stator

[0105] 3 air gap

[0106] 4 Rotor

[0107] 5 rotor bodies

[0108] 6 Rotor shaft

[0109] 7 rotor bearings

[0110] 8 Motor housings

[0111] 9 Coupling section

[0112] 10 Connection element

[0113] 11 Insulation element

[0114] 12 Stator mount

[0115] 13 Insulation element

[0116] 16 rolling elements

[0117] 17 Gear arrangement

[0118] 18 Rotation axis

[0119] 19 Warehouse sign

[0120] 20 Powertrain

[0121] 21 Motor vehicle

[0122] 22 Outer ring

[0123] 23 inner ring

[0124] 24 screw connections

[0125] 26 screw

[0126] 27 screw head

[0127] 28 spacers

[0128] 29 Access area

Claims

Claims 1. Electric axial flux machine (1), in particular for use within a drive train (20) of a hybrid or fully electric motor vehicle (21), comprising an annular disk-shaped stator (2) and at least one rotor (4) separated from the stator (2) by an air gap (3), with at least one annular disk-shaped rotor body (5) which is connected to an electrically conductive rotor shaft (6) in a torque-transmitting manner, wherein at least one electrically conductive rotor bearing (7) designed as a rolling bearing is arranged on the rotor shaft (6), by means of which the rotor shaft (6) is rotatably mounted relative to the stator (2), wherein at least one outer ring (22) of the rotor bearing (7) is connected to the rotor shaft (6) and at least one inner ring (23) of the rotor bearing (7) is connected to an electrically conductive bearing shield (19), and the bearing shield (19) is connected by means of at least one axially extending,electrically conductive screw connection (24) is fixed to an electrically conductive motor housing (8) in which the stator (2) and the rotor (4) are at least partially received, and the stator (2) is electrically insulated from the bearing shield (19), and the stator (2) is axially penetrated by the screw connection (24), characterized in that, at least one first electrical insulating element (13) is arranged between the bearing shield (19) and the screw connection (24), so that the bearing shield (19) is electrically insulated from the motor housing (8).

2. Axial flux machine (1 ) according to claim 1 , characterized in that in the penetration area (29) of the screw connection (24) through the stator (2) the stator (2) is electrically insulated from the screw connection (24).

3. Axial flux machine (1 ) according to claim 1 or 2, characterized in that the screw connection (24) has a screw (26) with a screw head (27) and the first electrical insulation element (13) is positioned between the screw head (27) and the bearing shield (19).

4. Axial flux machine (1 ) according to one of the preceding claims, characterized in that the stator (2) has at least one hollow cylindrical and electrically conductive spacer (28) extending axially through the stator (2), which is supported axially on one side against the housing (8) and / or on the other side axially against the bearing shield (19), wherein the spacer (28) is penetrated by the screw connection (24) and a second electrical insulating element (13) is arranged between the bearing shield (19) and the spacer (28), so that the bearing shield (19) is electrically insulated from the spacer (28).

5. Axial flux machine (1 ) according to one of the preceding claims, characterized in that in a plurality of screw connections (24) at least one electrical insulating element (13) is arranged between the bearing shield (19) and the respective screw connection (24), so that the bearing shield (19) is electrically insulated from the motor housing (8).

6. Axial flux machine (1 ) according to one of the preceding claims 4-5, characterized in that a plurality of the screw connections (24), preferably all screw connections (24) each extend through a spacer (28).

7. Axial flux machine (1 ) according to one of the preceding claims, characterized in that the first electrical insulating element (13) and / or the second electrical insulating element (11 ) is each designed as a disc-shaped insulating element, in particular as a ceramic disc, plastic disc, electrically insulating metal disc, coated plastic disc.

8. Axial flux machine (1) according to one of the preceding claims, characterized in that the first electrical insulating element (13) and / or the second electrical insulating element (14) are designed as a shim disk.

9. Axial flux machine (1 ) according to one of the preceding claims, characterized in that the first electrical insulation element (13) and / or the second electrical insulation element (11 ) are sleeve-shaped.

10. Powertrain (20) of a hybrid or fully electric motor vehicle (21) comprising an axial flux machine (1) according to any of the preceding claims.

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